1. Field of the Invention
The invention relates to a slot insulating paper arranged in a slot of a core of an electric motor or generator.
2. Description of Related Art
An electric motor is an electrical device that includes two portions and that causes relative motion between the two portions by causing interaction of a shifting magnetic field, formed by supplying electric power to one of the portions, with the other one of the portions. The portion that forms the shifting magnetic field includes a core and coils. The core has a yoke extending in a direction in which the magnetic field shifts and teeth protruding from the yoke and arranged in the magnetic field shifting direction. A portion between any adjacent two of the teeth is called slot. The coils are formed such that conductive wires are wound around the teeth, with the result that the coils are partially located inside the slots.
In contrast to the electric motor that converts electric energy to mechanical energy, that is, relative motion between two members, a generator is an electrical device that converts relative motion between two members to electric energy. The structure of the generator is substantially the same as the structure of the electric motor, and a device that functions as both the electric motor and the generator is also known. Hereinafter, the electric motor will be described as an example; however, it should be understood that the generator and the device that functions as both the electric motor and the generator are not excluded.
In order to ensure electrical insulation between the core and coils of the electric motor, an insulating paper (hereinafter, referred to as slot insulating paper) may be arranged along the surfaces of the core, which define each of the slots. The known slot insulating paper is not only a so-called “paper” obtained by straining plant-based fiber but also a sheet made of a resin or a sheet made of a mineral, such as mica. Japanese Patent Application Publication No. 2008-178197 (JP 2008-178197 A) describes a slot insulating paper formed by laminating sheet materials having different characteristics (for example, see paragraph 0012). In addition, Japanese Patent Application Publication No. 2010-115040 (JP 2010-115040 A) also describes a slot insulating paper having multiple layers. Furthermore, Japanese Patent Application Publication No. 4-210744 (JP 4-210744 A) and Japanese Patent Application Publication No. 2011-200046 (JP 2011-200046 A) describe a slot insulating paper that ensures the strength of a portion of a sheet-shaped material by folding the portion.